On the periodic table of elements, krypton is chemical element number 36. It is a member of the noble gases group of elements. Helium, neon, argon, xenon, and radon are the other noble gases. Krypton is a colourless, tasteless, and odourless gas under normal conditions. It has a density of about 0.5 oz per gallon (3.7 g per litre) at normal temperature and pressure, making it nearly three times heavier than air. Krypton can exist as a liquid or a solid at extremely low temperatures.
William Ramsay and Morris William Travers of University College, London, were convinced that the noble gas argon, extracted from air, was one of a new group of elements in the periodic table after discovering it. Others were likely to be hidden in the argon, so they hoped that by liquefying and evaporating it, it would leave behind a heavier component, which it did. On the afternoon of May 30, 1898, it yielded krypton, and they were able to isolate about 25 cm3 of the new gas. They immediately tested it in a spectrometer and discovered that it was a new element based on its atomic spectrum.
• Commercially, krypton is used as a filling gas for energy-saving fluorescent lights. It's also found in some high-speed photography flash lamps.
• It is reactive enough to form chemical compounds, unlike the lighter gases in its group. Krypton, for example, reacts with fluorine to form krypton fluoride. In some lasers, krypton fluoride is used.
• During the Cold War, radioactive krypton was used to estimate Soviet nuclear production. Because all nuclear reactors produce gas, the Russian share was calculated by subtracting the amount produced by Western reactors from the total in the atmosphere.
• The isotope krypton-86 was used to define the standard measure of length from 1960 to 1983. One metre was defined as 1,650,763.73 wavelengths of a line in the isotope's atomic spectrum.
• In fluorescent lights, krypton is combined with argon to improve brightness, and in incandescent lights, it is combined with nitrogen to extend their lifetime. It's also found in flashbulbs, which produce a very bright light for a very short time, making it ideal for high-speed photography. Small flaws in metal surfaces can be found using radioactive krypton-85. The gas tends to collect in these flaws, where it can be detected due to its radioactivity.
• Anesthetic properties limit xenon's fraction in the breathing gas to 35 percent, despite its potential for use in computed tomography (CT) to assess regional ventilation. A breathing mixture of 30% xenon and 30% krypton is comparable to a 40% xenon fraction in terms of CT effectiveness, while avoiding the negative effects of a high partial pressure of xenon gas.
• In nuclear medicine, the metastable isotope krypton-81m is inhaled and imaged with a gamma camera for lung ventilation/perfusion scans.
• Detection of clandestine nuclear fuel reprocessing facilities in North Korea and Pakistan has been done using krypton-85 in the atmosphere. These facilities, which were discovered in the early 2000s and were suspected of producing weapons-grade plutonium, were discovered.
• Occasionally, krypton is used as an insulating gas between window panes.
• Krypton is used as a propellant in SpaceX Starlink's electric propulsion system.
The fractional distillation of liquid air produces a number of valuable elements, including krypton. Nitrogen makes up more than three-quarters of the air we breathe. Nitrogen is used to make a wide range of chemical compounds, the most common of which is ammonia. Nitrogen is used to protect many substances from oxidation because it is much less reactive than oxygen. Freeze-drying and refrigeration both use liquid nitrogen.
Oxygen makes up about a fifth of the air we breathe. Steel is the world's largest consumer of pure oxygen. Excess carbon in the form of carbon dioxide is removed from steel using oxygen. Oxygen is also used in sewage treatment and solid waste incineration. Rocket fuel is made up of liquid oxygen.
Other than krypton, the noble gases argon, neon, and xenon can be obtained from air. Certain types of light bulbs contain argon. The familiar neon sign is created by passing an electric current through a glass tube containing neon under low pressure. Strobe lights use xenon to produce intense, short bursts of light.
The future of nuclear power production is likely to have an impact on krypton production. Nuclear power plants may become an important source of krypton in the future because krypton can be produced as a byproduct of nuclear fission. However, if nuclear fission is largely replaced by nuclear fusion or other forms of energy production, krypton will almost certainly remain a product of the atmosphere.